The present disclosure relates to an optical fiber fixing structure.
A semiconductor laser module outputting light from an optical fiber has an optical fiber fixing structure in which the optical fiber is inserted into and fixed to a metal pipe fixed to a semiconductor laser module package. The metal pipe and the optical fiber are fixed with an adhesive such as low melting point glass and hermetically sealed. Here, the thermal expansion coefficients of the metal pipe and the low melting point glass are larger than that of the optical fiber. Thus, stress is applied on the optical fiber.
Moreover, there is disclosed a polarization maintaining optical fiber that propagates light while maintaining the polarization plane of the light. The polarization maintaining optical fiber has a core and a cladding that is formed on the outer periphery of the core and includes a pair of stress imparting parts arranged in lateral regions to the core. In this polarization maintaining optical fiber, the stress imparting parts impart stress to the core, and a birefringence phenomenon due to stress is used to maintain a polarization plane. In such a stress imparting type polarization maintaining optical fiber, when stress is applied from the outside, stress imparted to the core is changed, which may deteriorate a polarization extinction ratio.
That is, the optical fiber fixing structure of a semiconductor laser module using a polarization maintaining optical fiber has a problem in that stress is applied on the optical fiber and a polarization extinction ratio is deteriorated. Then, there are disclosed structures that reduce stress applied to the polarization maintaining optical fiber from the outside and suppress deterioration of a polarization extinction ratio (see Japanese Laid-open Patent Publication No. 62-299918, Japanese Laid-open Patent Publication No. 2007-264346 and Japanese Laid-open Patent Publication No. 6-67038, for example).
However, birefringence is considerably sensitive to stress, and there has been a problem in that a polarization extinction ratio is deteriorated when the polarization maintaining optical fiber deviates from the center of a hole of a metal pipe.
There is a need for an optical fiber fixing structure in which the deterioration of a polarization extinction ratio is suppressed.